D810 and shutter speed

I read always, that on surface the D810 has a problems with by normal shutter speeds, and the new 1/125 should be 1/200 to avoid receiving no sharpness.

While diving with my D810 in Nauticam / Zen 170 and Sigma Fisheye I havent identified this effect when using 1/125 shuter speed......can this be an effect from flash? Is the flash speed maybe freezing the picture?